The present invention relates to a method for producing tetraketones of a type which are themselves useful in the production of thermally stable quinoxaline polymers.
Polyquinoxaline resins have become widely sought after in recent years due to their unique thermal properties. Because of their desirable properties, the polymers are useful for high temperature adhesives, coatings and films in a number of critical industries. As stated in Stille, U.S. Pat. No. 3,661,850, polyquinoxaline polymers are "suitable for high temperature electrical insulators, battery separators, foams, ablative materials for re-entry bodies and rocket nozzles". Other patents which discuss these unique resins, their properties, and uses are: Augl, U.S. Pat. Nos. 3,766,141 and 3,642,700; and Hergenrother, U.S. Pat. No. 3,778,412.
Stille, Augl and Hergenrother all disclose methods of preparing polyquinoxalines from tetraketones of the following general formula: ##STR2## In Stille R is said to be selected from the group consisting of alkyl, aryl, alkaryl, and aralkyl groups and hydrogen, while R' is selected from the group consisting of alkylene, arylene, aralkylene and alkarylene groups (Col. 3, lines 6-16). Similarly in Augl, R is listed as C.sub.6 H.sub.5 or H and R' is m-phenylene, p-phenylene or a number of diphenyl compounds (Col. 2, lines 29-64 of U.S. Pat. No. 3,766,141). In Hergenrother, R is stated to be hydrogen, alkyl, phenyl and substituted phenyl and R' is for the most part selected from a number of divalent alkyl, phenyl and diphenyl compounds (Col. 3, lines 1-34).
These prior art patents also list several methods of preparing the desired tetraketone precursors used in the manufacture of the polyquinoxaline resins. Included are the methods described in Helv. Chim. Acta., 27, 496 (1939), Helv. Chim. Acta., 24 899 (1941) and Bull. Soc. Chim. France, 636 (1956) (Stille, Col. 5, lines 9-24), and those in Hergenrother and Augl, (Hergenrother, Examples 3-5; Augl, Col. 3, lines 3-36), all of which disclose methods wherein diketones are oxidized to tetraketones with selenium dioxide or selenious acid. These reagents, however, are reduced during the reaction to selenium metal which is highly toxic and extremely difficult to remove from the reaction mixture. The reagents are also expensive.
As noted in Wentworth, U.S. Pat. No. 3,839,497, expense in preparation of the tetraketone precursor has resulted in current high costs for the polyquinoxaline resins. Accordingly, Wentworth suggests an alternative method for producing 1,4-bis(phenylglyoxaloyl) benzene. That method involves reacting cuprous phenylacetylide and p-diiodobenzene to form p-bis(phenylethynyl) benzene which is then placed in a reaction chamber with N-bromosuccinimide and a dimethylsulfoxide solvent and oxidizing agent. A p-bis(phenyl glyoxaloyl) benzene precipitate is formed.
While this method is a possibility, is still does not appear to offer a feasible way of obtaining large quantities of tetraketones rapidly and inexpensively.
Thus, the production of tetraketones by the prior art processes has been limited. Therefore, the need exists for an improved process for producing large quantities of tetraketones as inexpensively as possible.